Oscillator



Jan. 10, 1933; v, E: w n- 1,893,813

OSCILLATOR Filed April 9, 1932 INVENTOR VERNON E. WHITMAN ATTORNEYS when tuned to receive signals of three distinct circuits.

atented fan. 10, 1933 I rsaasis PATENT GICE VERNON E. WHITMAN, OF NEW YORK, N. 52., ASSIGNOR' '10 HAZIELTINE CORPGRATION OSCILLATOR Application filed April 9, 1932. Serial No. 604,172.

This invention relates to oscillator-modulator systems, and more particularly to such systems, for use in heterodyne radio receivers, having substantially uniform output of any frequency within a specified band.

In accordance with the present invention, a uniformoutput is obtained in an oscillatormodulator, tunable over a considerable frequency range, by the combination of uniform gain circuits and neutralization of the cathode-grid capacity.

The features of the present invention are shown and "described hereinafter in connection with a superheterodyne radio receiver, although this invention is also useful in connection with receivers of the heterodyne type, and in connection with any oscillator-modulator arrangement required to operate over a considerable frequency band, where it is de sired to maintain substantially uniform output without necessitating adjustments, other than the tuning.

For convenience, the oscillator-modulator will hereinafter be considered as composed The circuit connected between the grid and the cathode of the tube, and including an inductance shunted by a tuning condenser, will be considered the input circuit. That circuit connected between the plate and the cathode of the tube, and including the output inductance'and the condenser which tunes it to the intermediate frequency, will be referred to as the output circuit. The closed oscillatory circuit, which includes an inductance and a tuning condenser which is adapted to tune the inductance to the oscillation frequency, will be referred to as the oscillation circuit. This latter circuit is coupled both to the output circuit and to the input circuit. That portion of the input circuitwhich is common to the output circuit will be referred to as the cathode circuit; That portion of the inpht circuit'comprising the inductance shunted by the tuning condenser will be referred to as the tuned input circuit.

That voltage in the input circuit of the oscillator-modulator tube impressed therein by the oscillation circuit will be referred to hereinafter as the oscillation voltage. That voltage impressed in the input circuit of the oscillator-modulator tube from the antenna or other input at the frequency of the signal carrier will be referred to hereinafter asthe signal voltage. The'ratio of the alternatingcurrent voltage fluctuations in the secondary of the output transformer of the oscillatormodulator tube to the signal voltage fluctuations in the input thereof will be referred to hereinafter as the translation gain of the oscillator modulator.

A problem common to all oscillators is to obtain a uniform output when the oscillator is required to be tuned through a broad band of frequencies. When an oscillator is combined with a modulator, as, for instance, in a heterodyne or superheterodyne radio receiver, the problem of obtaining substantially constant translation gain in the oscillatormodulator is rendered more difiicult. It has been observed, as will be demonstrated hereinafter, that the presence of a circuit tuned to a frequency near the oscillation frequency and connected in the input of such a tube, causes a reduction of the oscillation-frequency voltages which are supplied to the oscillator-modulator tube input terminals.-

This reduction of feedback energy increases toward the high-frequency end of the tuning range. I

In the usual oscillator-modulator arrangement, wherein the oscillation voltage is fed into the cathode circuit, a large part of the oscillation Voltage appears across the tuned input circuit; As the frequency of oscillation is normally above that of the signal, the oscillator circuit acts as an inductive load in the signal circuit and tends to increase re-' generation.

It is the object of the present invention to overcome the above-noted difficulties and to produce and oscillator-modulator circuit vide some means to prevent radiation of the Oscillation frequency through the tuned input circuits, which radiation would cause interference in nearby receivers. This is gen-' 5 erally accomplished by provision of a unidirectional coupling tube, which prevents the radiation of the oscillation-frequency currents which are impressed in the input circuit of the modulator. A system of that nature is shown in patent of L. A. Hazeltine, No. 1,869,894, of August 2, 1932. Such a provision, however, can not, in an oscillatormodulator circuit, prevent the reaction of the tuned input circuit of the modulator upon the oscillation currents, occasioned as above noted, which reaction it is the primary object of this invention to prevent.

It is, however, an important feature of this invention to prevent the radiation of oscillation-frequency currents without requiring the use of a coupling tube.

These and further objects of the invention will become apparent from the following specification taken in connection with the accompanying drawin In accomplishin tie objects of the present invention, the gri -cathode capacity of the oscillator-modulator tube is neutralized by the use of a neutralizing condenser and winding inductively coupled to the oscillation circuit inductance. This neutralizing arrangement is combined with means for maintaining a substantially uniform oscillation voltage in the oscillation circuit and a substantially uniform coupling between the oscillation circuit and the cathode circuit.

This arrangement simultaneously serves to prevent the reduction of feedback voltage in the oscillator circuit due to the capacitive grid circuit, to prevent radiation of the oscillation-frequency currents, and to prevent regeneration in the signal circuit at the signal frequency due to the inductive load of the os cillator circuit in the plate circuit of the tubes.

A preferred method for maintaining uniform oscillation voltage is to provide. a resistor shunting a portion of the impedance of the oscillation circuit. The dissipation in this resistor increases as the oscillation voltage increases, or at the high-frequency end of; the tuning range, thus assisting in maintaining constant oscillation voltage. Having thus briefly described the present invention, attention is invited to the accompanying drawing, in which: Fig. 1 is a diagram of an elementary circuit to assist in explaining the effect of the tuned input circuit upon the oscillation voltage impressed in the oscillator-modulator input;

Fig. 2 is an elementary circuit diagram of an oscillator-modulator arrangement for obtaining substantially constant translation 66 .gain by means of the combination of a resistor in the oscillation circuit and grid-cathode neutralization;

Fig. 3 is an elementary circuit diagram of an oscillator-modulator.arrangement for obtaining substantially constant translation 70 gain by means of dual feedback couplings in the oscillation circuit and by grid neutralization.

In Fig. 1 there is represented a simplified oscillator-modulator input circuit. The tube 5 has the tuned circuit 2, comprising the inductance L and the capacitance C, connected between its grid and cathode. The capacitance C is composed of the tuning condenser 3 and the grid-cathode capacity of the tube 5, so represented as C The oscillation voltage e is fed to the circuit by means of the cathode inductance 4. The frequency of the oscillation voltage being, as is the usual case, above that of the signal currents to which the circuit 2 is tuned, the latter circuit is capacitively reactive to the oscillation voltages, and the circuit 2 is therefore symbolized as having a capacity C.

The voltage at the oscillation frequency impressed across the grid-cathode of 5 is represented by e which is given by the following equation:

' C m (1) Now the apparent parallel capacitance of the circuit 2 is given by the equation:

and

w, L where s is the frequency of the signal and (n is the oscillation frequency. Assuming, then, a signal frequency of 600 kc, an oscil lation frequency f =77 5 kc, and that GFiM/ fi On the other hand, assuming a signal frequency of 1500 kc with f =1675 kc,

This decrease in feedback voltage as the circuits are tuned to the high frequency end of the band, causes a sharp falling oil in oscillator amplitude and oscillator-modulator translation gain, which eiiect is overcome, in accordance 7 with the present invention, by neutralizing the grid-cathode capacity. l Vith the capacity 0 0 the voltage e always equals the voltage a as the capacitive reactance or" the tube will then always be high with respect to that of the tuned circuit.

Fig. 2 shows the input of a superheterodyne radio receiver in which means are provided tor neutralizing the grid-cathode capacity of the oscillator-modulator tube 11. This circuit comprises an input including the tuned circuit 13, coupled to the antenna circuit 15, the output circuit including the tuned circuit 17, coupled to the tuned input 19 of the first intermediate-frequency amplifier, the oscillation circuit 27 and the neutralization circuit.

The input circuit is connected between the grid of the tubell and the cathode thereof and includes, besides the tuned circuit 13, tuned by means of the variable condenser 12, the biasing resistor 24 shunted by the condenser 25, and the-upper part of the inductance coil 23. The resistor 24, condenser 25, and the upper part of coil 23 are also included in the output circuit, and the flow of plate current through the resistor serves to bias the tube 11 to the proper point to permit efiicient modulation.

The output circuit, which is connected between the plate electrode of the tube 11 and the cathode thereof, comprises the radio-frequency choke 21, the tuned output circuit 17 thehigh-potential source 22, and the cathode circuit mentioned above.

The oscillation circuit 27 comprises the inductance 28, the tuning condenser 30, and the alignment condenser 31. The alignment condenser permits the condenser 30 and the condenser 12 of the tuned circuit 13 to be similar and to be connected, as indicated, for uni-control operation.

The oscillation circuit is coupled to the output circuit by means of the capacity between the open-end coil 33, directly connected to the plate electrode of the tube 11, and the upper end of the inductance 28. The osc llation circuit is coupled to the input circuit by the inductive coupling between the inductance 28 and the part of the inductance 23 which is included in the cathode circuit.

The neutralizing arrangement comprises the connection from the lower end of the inductance 23 through the neutralizing condenser 35 to the grid of the tube. This arrangement tends to cause a voltage whichis equal and opposite to that which would be impressed thereon by the cathode variations, due tothe gridscathode capacity, to be im pressed upon the grid. Thus grid voltage variations at the oscillation frequency are prevented.

The screen electrode of the tube 11 is supplied with an appropriate potential by means of the connection to an intermediate point on the voltage source 22.

The capacity coupling between the coupling coil 33 and the inductance 28 increases with frequency, and, as the reactance of the coil 28 also increases with frequency, the high-frequency voltage across this coil will likewise increase at the higher frequencies.

Inasmuch as the effective inductive coupling between the coil 23 and the oscillation inductance 28 also increases with frequency, a considerable variation in the oscillation voltage impressed upon the input circuit would be obtained as the circuits were tuned through any appreciable frequency band. The res'stor 29, however, will serve to by-pass an increasing proportion of the current as the frequency of oscillations is increased. By properly proportioning all of the component parts of this circuit, this eiiect may be so adjusted as to permit impressing substantially constant voltage fluctuations upon the cathode of the tube 11 as the circuit is tuned throughout a predetermined frequency band.

The input circuit of Fig. 3 is similar to that of Fig. 2, like parts being des'gnated by the same reference characters.

The output of the tube 11 of Fig. 3 comprises two paths, one of which includes resistor 18, coupling condenser 26, inductance 20, which is inductively coupled to the inductance 28 of the oscillation circuit 27 and the condenser 31 of the oscillation circuit. The coupling between inductance 20 and inductance 28 is so adjusted relative to the coupling between the output circuit and the oscillation circuit, produced by the condenser 81, that a dual-coupling effect is produced which will maintain a substantially uniform oscillation voltage throughout the frequency band.

The other branch of the output circuit in cludes resistor 18, the output inductance 16, and the high-potential source 22. The output inductance 16 is tuned by the conjoint action of the coupling condenser 26 and the alignment condenser 31 to be responsive to signals of the intermediate frequency.

The condenser 31 is so proportioned relative to the other circuit elements as to maintain alignment between the oscillation and tuned circuits as these circuits are simultaneously tuned by a uni-control arrangement, as designated by the dotted line connecting their respective tuning condensers.

The dual-coupling feedback arrangement, which assists in maintaining a uniform outp'ut,'has been described more fully in copend ing application of Harold A. Wheeler, Serial No. 587,681, filed January 20, 1932.

Inductively coupled to the output inducmay be provided, such, for instance, as a variable resistor connected between the an tenna and ground.

In operation, the connection from the lower end of inductance 23 to the grid of the tube through the condenser 35, which latter isappropriately adjusted, serves to neutralize the capacity between the grid and cathode, and therefore, as above noted, the feedback voltage induced by the oscillation circuit 27 into the cathode circuit will be unaffected by the presence of the tuned circuit 13, and as the oscillation voltage is substan tially constant, a substantially constant feedback voltage will be impressed upon the input circuit of the tube 11.

Vhereas screen-grid heater-type tubes have been shown and described, it is to be understood that any appropriate tubes may be substituted therefor.

\Vhat is claimed is:

1. In an oscillator-modulator arrangement, a vacuum tube having grid, anode, and cathode, an input circuit connected between said grid and said cathode, an output circuit connected between said anode and said cathode, a tuned circuit included in said input circuit and tunable to the frequency of a current to be modulated, an oscillation circuit coupled to said output circuit and tunable to the frequency'of a modulating current, means for impressing voltages of said oscillation frequency upon the input circuit of said tube, means for producing substantially constant amplitude of oscillation voltage as i said oscillation circuit is tuned throughout a range of frequencies, and meansfor neutralizing the grid-to-cathode capacity of said tube relative to the oscillation-frequency input thereof, whereby the presence of the tuned input circuit will not affect the oscillation-frequency voltage impressed upon the input of said tube.

2. In an oscillator-modulator arrangement, a vacuum tube having grid, anode, and cathode, an input circuit connected between said grid and said cathode, an output circuit connected between said anode and said cathode, a tuned circuit included in said input circuit and tunable to the frequency of a cur .rent to be modulated, an oscillation circuit coupled to said output circuit and tuned to y the frequency of a modulating current, a conpling between said oscillation circuit and said input circuit, means for producing substantially constant amplitude of oscillation voltages in said oscillation circuit as it is tuned throughout a range of frequencies, said means including a resistor shunted across a portion of the impedance of said circuit, and

' a neutralizing connection for neutralizing the grid-to-cathode capacity of said tube relative to the oscillation-frequency input thereof, whereby the presence of the tuned input circuit will not affect the oscillationfrequency voltage impressed upon the input of said tube, and therefore said tube has a substantially constant translation gain as said tuned circuit and said oscillation circuit are simultaneously tuned throughout a range of frequencies.

3. In an oscillator-modulator arrangement, a vacuum tube having grid, anode, and cathode, an input circuit connected between said rid and-said cathode, an output circuit connected between said anode and said cathode, a tuned circuit included in said input circuit and tunable to the frequency of a current to be modulated, an oscillation circuit coupled to said output circuit and simultaneously tunable to a frequency differing by a constant amount from that to which said tuned input circuit is tuned, a tuned circuit included in said output circuit and tuned to the frequency difference of said oscillation and tuned input circuits, means for producing a substantially constant amplitude of oscillation voltage in said oscillation circuit as it is tuned throughout a range of frequencies, means for impressing said oscillation voltages upon the input of said tube, and means associated with said last-mentioned means for neutralizing the tube input capacity relative to the oscillation-frequency input thereof, whereby said tube will have a substantially uniform translation gain as said circuits are tuned throughout a band of frequencies.

4. In an oscillator-modulator arrangement, a vacuum tube having grid, anode, and cathode, an input circuit connected between said grid and said cathode, an output circuit connected between said anode and said cathode, a tuned circuit included in said input circuit and tunable to the frequency of a current to be modulated, an oscillation circuit coupled to said output circuit and tuned to the frequency of a modulating current, said coupling comprising dual couplings so proportioned that substantially uniform voltages are produced in said oscillation circuit as it is tuned throughout a range of frequencies, means for impressing said oscillation-frequency voltages upon the input of said tube, and means for neutralizing the grid-to-cathode capacity of said tube relative to the oscillation-frequency input thereof, whereby said tube will have a substantially uniform translation gain as both said tuned aeeaera input circuit and said oscillation circuit are simultaneously tuned throughout a band of frequencies.

5. In a superheterodyne radio receiver, an scillator-modulator arrangement comprising a vacuum tube, an oscillation circuit, tunable to produce oscillations covering any of a band of frequencies, coupled to the input and output of said vacuum tube, the coupling between said output and said circuit being of a type adapted to give uniform voltage transfer as the frequency of oscillations is changed, and means associated with the coupling between said oscillation circuit and the input of said tube for neutralizing the grid to-cathode capacity of said tube to render the oscillation voltage impressed upon said tube substantially uniform as said oscillation circuit is tuned.

6. In a superheterodyne radio receiver, an oscillator-modulator circuit comprising a vacuum tube, an oscillation circuit coupled to the input and output of said vacuum tube, said oscillation circuit comprising inductive and capacitive reactances, a resistor shunted across a portion of the reactances of said circuit, whereby the oscillation voltage across the output reactance thereof is rendered substantially uniform as said circuit is tuned, and means associated with the coupling of said circuit tothe input of said tube for neutralizing the capacity between the cathode and grid thereof relative to the oscillation voltages, whereby said oscillator modulator will have a substantially uniform translation gain throughout a band of frequencies.

7. In a superheterodyne radio receiver, an oscillator-modulator circuit comprising a vacuum tube, an oscillation circuit coupled to the input and output of said vacuum tube, said oscillation circuit comprising inductive and capacitive reactances, inductive and capacitive elements coupling said output and said oscillation circuits, whereby the oscillation voltage across the output reactance thereof is rendered substantially uniform as said circuit is tuned, and means associated with a coupling of said circuit to the input of said tube for neutralizing the capacity between the cathode and grid thereof relative to the oscillation voltages, whereby said oscillator modulatorwill have a substantially uniform translation gain throughout a band of frequencies.

8. In a superheterodyne radio receiver, the combination with an oscillator-modulator circuit which includes a vacuum tube, of a uniform voltage oscillation circuit, tunable to produce oscillations covering any of a band of frequencies, coupled to the input and output of said vacuum tube, and means to neutralize'the grid-to-cathode capacity of said tube relative to the oscillation voltage thus produced, whereby said circuit will have a substantially uniform translation gain as the oscillation circuit is tuned throughout a band of frequencies.

9. ln an oscillator-modulator system which includes a vacuum tube having input, output, and oscillation circuits associated therewith, the method of obtaining substantially uniform translation gain in said tube when operating over a considerable band of frequencies, which comprises producing a substantially constant voltage in the oscillaand oscillation circuits to give a substantially uniform oscillation voltage in said oscillation circuit. and nuetralizmg the input capacity of said tube relative to the oscillation voltage, whereby the varying effect of the input circuit upon said oscillation voltage is eliminated.

11. in an oscillator-modulator arrangement which comprises a vacuum tube havin input, output, and oscillation circuits, sai oscillation circuit comprising inductive and capacitive reactances, the method of obtaining substantially uniform translation gain in said tube when operated to modulate a current of any one of a band of frequencies,

which comprises by-passing a varying portion of the oscillation voltage relative to one of said reactances, whereby the voltage in the other of said reactances will remain substantially uniform throughout the tuning range of said device, and neutralizing the input capacity of said tube relative to the oscillation feed-back voltages, whereby the efiect of the remainder of the input circuit upon the oscillation voltages is eliminated.

' 12. An electric circuit arrangement including a vacuum tube having grid, anode; and cathode elements, input, output and oscillation circuits therefor, uni-control means for tuning said input and oscillation circuits over a range of frequency, reactive elements, the efiect'of which is variable with frequency, associated with said oscillation circuit, whereby the oscillation voltage is maintained uniform as said tuning is swept over a frequency range, and means for preventing undesirable absorption of said oscillation voltage by said input circuit, said means comprising a capacity and coil connected in series between the gridand cathode of said tube.

13. An electric circuit arrangement including a vacuum tube having grid, anode, and

cathode elements, input, output, and oscillation circuits therefor, uni-control means for tuning said input and oscillation circuits over a range in frequency, reactive elements, the effect of which is variable with frequency as said tuning is swept over a frequency range, associated with each of said circuits, and means for preventing undesirable absorption of said oscillation voltage by said input circuit, said means comprising a capacity and coil connected in series between the grid and cathode of said tube.

14. An electric circuit arrangement including a vacuum tube having grid, anode, and cathode elements, input, output, and oscillation circuits therefor, uni-control means for tuning said input and oscillation circuits over a range in frequency. reactive elements, the effect of which is variable with frequency, associated with said oscillation circuit for causing a variation of the oscillation voltage as the oscillator circuit is tuned over a range in frequency to compensate for the variation of the input voltagedue to the change of the reactance of the input circuit as the input circuit is simultaneously tuned, and means for preventing undesirable absorption of said oscillation voltage by said input circuit, said means comprising a capacity and coil connected in series between the grid and cathode of said tube, whereby there is produced a modulator circuit in which the conversion gain is uniform as the device is tuned over a range in frequency. I

In testimony whereof I aifix m signature.

VERNON E. VV H ITMAN. 

